Method and device for thermally treating objects

ABSTRACT

The invention relates to a method and to a device for thermally treating objects. The aim of the invention is to facilitate a better control of the temperature profile of an object to be thermally treated. To this end, the invention provides a method and a device for thermally treating an object in a heating system, especially for treating semiconductor wafers ( 2 ) in a rapid heating system ( 1 ). The objects are thermally treated at a predetermined temperature progression and the temperature of the object is controlled via a PID control and a feedforward control that are based on a simulation model of the heating system and the object. Said model consists of individual models of components of the heating system and/or the object. The parameters of at least one of the individual models are monitored during the thermal treatment and the model is adapted to the monitored parameters.

[0001] The present invention relates to a method and an apparatus forthe thermal treatment of objects in a heating unit, especiallysemiconductor wafers in a rapid heating unit, according to which theobjects are thermally treated with a prescribed temperature course, andthe temperature of the object is regulated with an appropriatetemperature regulation, e.g. a PID regulation and a forward-actingcontrol that is based upon a simulation model of heating apparatus andobject.

[0002] Such methods and apparatus are known in the art. For example, inthe semiconductor industry for the manufacture of electronic components,it is customary to thermally treat disk-shaped semiconductor substratesvia heat lamps having high heating rates of more than 100° C. persecond. In this connection, the thermal treatment generally follows aprescribed chronological temperature profile. To achieve thistemperature profile, a regulation of the heating power emitted from thelamps is necessary. Since the heating lamps are controlled with aprescribed power profile, the wafer temperature follows a specifictemperature curve. However, in this connection one must take care thatbetween the radiated power given off from the lamps and the temperatureof the wafer there is no linear relationship, which is attributable todifferent effects, in particular the Stefan-Boltzmann principle, (asdescribed, for example, in U.S. Pat. No. 4,761,538), but also, forexample, the shape of a process chamber, the arrangement of variouselements within the process chamber, the position of the wafer relativeto the heating lamps, etc. Therefore, a simple control of thetemperature profile via a prescribed control of the lamps is notpossible.

[0003] For this reason, there is effected a constant monitoring of thewafer temperature at any given time along with simultaneous readjustmentthereof if there is a deviation from a theoretical temperature value. Inthis connection, two different regulating processes are utilized, namelya closed temperature regulating circuit, e.g. a PID regulation on theone hand, and a so-called forward-acting control on the other hand.

[0004] In the following, one should speak of regulation if at least oneparameter of a system should be brought to a value (or within aninterval about this value), whereby this parameter is conveyed back to aregulating apparatus so that the regulating apparatus can adjust thedesired value; as optimally as possible as a function of the observedparameter of the system. In this connection, the parameter can bedetected directly in the system, for example by measurement, although itcan also result, for example, from a model that reproduces the system inas good a manner as possible. Here one speaks of model-based regulation.Similarly, with systems that are regulated with regard to severalparameters, a combination of model-based and first-mentioned return ofthe parameters can be present. In general, one designates the return ofsuch parameters as feedback coupling.

[0005] In contrast to the regulation, with the control the parameters ofthe system that are to be controlled are not returned to a controldevice. The parameters that are to be controlled are determined with thecontrol device, e.g. by a model, and/or are controlled via some otherparameter than the parameter that is to be controlled.

[0006] With a closed temperature regulating circuit, the actual value ofthe wafer temperature at any given time is compared with a prescribedtheoretical or desired value. If deviations occur between the twovalues, a regulating apparatus becomes effective and takes care of anadjustment of the two values by more or less controlling, for example,the heating lamps. The greater the regulating difference is, the greateris the readjustment. Drawbacks of this regulation are a) that theregulating device is not informed about future changes of thetheoretical value, and b) that the wafer characteristics are not takeninto consideration, which can vary during the regulating process, forwhich reason such a regulation cannot react in an anticipatory manner.

[0007] These drawbacks are compensated for by a forward-acting controlthat in addition to a previous development, namely the theoretical valueand the actual value at any given time, also draws in the futuredevelopment of the theoretical value into the regulating process. As aconsequence, the adaptation of the actual value to the theoretical valuebecomes more precise, since the regulating apparatus draws in futurechanges of the theoretical value into the regulation.

[0008] For an even more precise regulation, a future property of thetheoretical value is calculated in advance, and in particular with theaid of a simulation model comprising heating apparatus and object orwafer that is to be treated. In this case, one speaks offorecast-regulated processes. Since the thermal capacities of individualchamber components are known, and it is known which lamp power isradiated into the chamber, the wafer temperature, as well as its futuredevelopment, can be estimated in advance by the forecast of thesimulation model as a function of the progress of the profile of theheating power.

[0009] This estimation, which up to now was effected upon a rigidsimulation model, is, however, very difficult, since the differentcomponents in the process chamber, including the heating apparatus andthe object that is to be treated, represent a non-linear system. Despitethese difficulties, with this method the adaptation of the course of thewafer temperature to the threshold profile can be improved.

[0010] As already mentioned, such simulation models treat the chamberwith all of its individual components and the wafer together as onesystem. There is no distinction between individual system components.Furthermore, the previously known simulation models are established onetime and are subsequently not altered, especially not during a process,i.e. while the object experiences a temperature-time treatment.Alterations within the system, for example during the treatment ofdifferent wafers (objects) having different optical characteristics,cannot be taken into account. In particular, alterations caused byprocess progress and/or by aging, such as, for example, the radiationgiven off by a heating lamp or other alterations within the chamber,cannot be taken into account. Changes caused by the progress of theprocess are, for example, heating up of the process chamber, which ismade, for example, of quartz glass, and the thermal radiation thatadditionally results therefrom and that is in a wavelength spectrum thatin general differs from that of the lamp radiation.

[0011] Proceeding from this state of the art, it is therefore an objectof the present invention to provide a method and an apparatus for thethermal treatment of objects in a heating unit that enables a betterregulation of a temperature profile of an object that is to be treated.

[0012] Pursuant to the present invention, this object is realized inthat the simulation model includes at least one individual model thatincludes components of the heating apparatus and/or of the object, andin that at least one parameter of at least one of the individual modelsis monitored during the thermal treatment and in that the simulationmodel is adapted to at least one of the monitored parameters. Thisresults in the advantage that the simulation model can be dynamicallyadapted to varying operating conditions, such as, for example,alteration of the heating power of the lamp due to age, objects havingdifferent optical characteristics, etc. Due to the adaptation of thesimulation model, a more precise regulation of the temperature curve ofthe object that is to be treated is in particular also possible for thereason that advantageously alterations that are due to the progress ofthe process, such as, for example, the aforementioned heating up of, forexample, process chamber (especially also the quartz componentscontained therein) can also be taken into consideration during thetemperature regulation. This can be utilized advantageously, forexample, for the reduction of the so-called “first wafer” effect. Thisinvolves the influence of the process chamber temperature upon theprocess result during the processing of wafers if, for example, duringthe processing of the first wafer the process chamber has not yetreached its average “operating temperature”. This effect always occursat the beginning of, for example, a mass production, or if between theprocessing of individual wafers there is so much time that the processchamber can cool off to temperatures that are below that of, forexample, mass production. As a result, due to the equipment, the processresults can be a function of the throughput of the wafers, which ofcourse is not desired. Pursuant to one preferred embodiment of theinvention, the object is irradiated with at least one heating lamp of aheating device. An individual model having at least one monitoredparameter is preferably provided for at least one heating lamp of theheating device, and operating parameters of the heating lamp, inparticular the irradiated heating power in relation to the controlpower, are monitored in order to discover alterations and if necessaryadapt the simulation model.

[0013] Pursuant to a further preferred embodiment of the invention, anindividual model is provided for the object that is to be treated, andparameters of the object that is to be treated, especially opticalcharacteristics thereof, are monitored in order to undertake, ifnecessary, an adaptation of the simulation model. Of particularsignificance are the absorption characteristics (or in general theoptical characteristics such as transmission, absorption or reflection)of the object that is to be treated or the coupling to the heatradiation at different temperatures, which can greatly influence theregulation, especially a forward-acting control, since thesecharacteristics are greatly temperature dependent for, for example, Siwafers. The parameters are preferably separately determined from oneanother on opposite sides of the object.

[0014] For a further optimization of the overall model, the datatransmission times and/or the computing times are determined andindividual models provided herefor are adapted to the determined values.With some measuring devices, such as, for example, pyrometers, atemperature determination of the object is not possible, or is onlypossible with great difficulty, below 400° C. Therefore, thetemperatures of the object under 400° C. are preferably calculated at alater stage with the aid of the simulation model, and this calculatedinformation is taken up in the regulation.

[0015] The object of the invention is also realized with an apparatusfor the thermal treatment of objects, especially semiconductor wafers,with a heating device, especially a rapid heating device, a regulatingunit having a temperature regulator, and a forward-acting control thatutilizes a simulation model of heating apparatus and object, in that amonitoring unit is provided for the sensing of parameters of componentsof the heating device and/or of the object, which parameters arerelevant for the simulation model, for the comparison of the measuredparameters with the parameters of the simulation model and for theadaptation of the parameters of the simulation model to the measuredparameters. With this apparatus there result the advantages alreadymentioned above with reference to the method.

[0016] The invention will be explained in greater detail subsequentlywith the aid of the drawing; in the drawing there is shown:

[0017]FIG. 1 Schematically the structure of a heating apparatus for thethermal treatment of objects;

[0018]FIG. 2 A graph of a theoretical and an actual temperature profileduring a thermal treatment of a semiconductor wafer with PID regulation;

[0019]FIG. 3 A graph for the determination of the radiation generatedfrom a lamp;

[0020]FIG. 4 A graph of a lamp model in a regulating circuit;

[0021]FIGS. 5a, b Curves that show the lamp radiation during voltagejumps without radiation regulator during a heating up phase or during acooling off phase.

[0022]FIGS. 6a, b Curves similar to those of 5 a and b that show thepower jumps with radiation regulators;

[0023]FIG. 7 A graph of a preliminary control unit;

[0024]FIG. 8 A graph of an expanded preliminary control unit.

[0025]FIG. 1 schematically shows the structure of a heating apparatus 1for the thermal treatment of semiconductor wafers 2. The apparatus 1 hasan inner process chamber 3 that is generally made of quartz glass and isprovided with support elements 5 for receiving the semiconductor wafer2.

[0026] Provided above and below the process chamber 3 are banks of lamps7 and 8 that are formed by a plurality of rod-shaped lamps, such as, forexample, tungsten-halogen lamps or arc lamps. However, it is alsopossible to provide only a single bank of lamps, e.g. for heating anobject on one side. Of course, other lamps can also be used. For thethermal treatment of the wafer 2, the lamps are controlled in such a waythat they give off a specific electromagnetic radiation that can becontrolled not only with regard to the spatial and/or spectralcomposition thereof, but also with regard to the intensity thereof.

[0027] During the thermal treatment, the temperature of the wafer ismeasured. For this purpose, two pyrometers are provided, a lamppyrometer 10 on the one hand and a wafer pyrometer 11 on the other hand.The lamp pyrometer 10 measures the electromagnetic radiation intensityI₀ given off by at least one lamp, while the wafer pyrometer 11 measuresthe radiation intensity I_(w) given off from the wafer 2 as well as aradiation intensity I_(r) reflected at the wafer 2, and possibly also aradiation transmitted through the wafer. The radiation intensity I₀given off by the lamps has a certain modulation that is either active,i.e. by directed, defined and/or controllable modulation of theradiation, or passive, i.e. achieved by utilization of system-dictatedradiation changes, that result, for example, from the frequency of thevoltage supply. This modulation can also be recognized in the radiationintensity I_(R) reflected at the wafer 2, and therefore that portion ofthe thermal radiation measured at the wafer pyrometer 11 that isactually given off from the wafer 2 can be determined in a signalanalyzer 12 to which are conveyed not only the signals of the lamppyrometer 10 but also of the wafer pyrometer 11. Details of thismeasuring method are described, for example, in DE-A-198 55 683, whichis attributable to the same applicant, and to which reference is made tothis extent in order to avoid repetition. The temperature measured inthis manner is compared with a desired wafer temperature in connectionwith, for example, a PID regulation, a regulation value for the banks oflamps 7,8 is determined, and they are accordingly controlled.

[0028]FIG. 2 shows the theoretical or desired temperature curve A andthe actual temperature curve B of a wafer during a conventional thermaltreatment. The dashed-line curve A shows the desired or theoreticaltemperature curve for the wafer, and the solid-line curve B shows theactual temperature curve of the wafer. The dashed-line curve initiallyshows a constant temperature T₀ that increases at a constant rate, forexample of 100° C. per second, in a time interval between t₀ and t₁ to atemperature T₁, and subsequently remains constant at this temperature.With the above-described regulation according to the state of the art,e.g. with a pure PID regulation, the actual temperature curve of thewafer does not follow this linear curve. Rather, heating up of the waferstarts only at a later point in time than is the case with thetheoretical curve. The heating up rate for the actual curve is thengreater than that with the theoretical curve, and the actual curve goesbeyond the desired end temperature T₁ of the wafer and levels out at thedesired final temperature T₁ only sometime after the point in time T₁.

[0029] As previously mentioned, the differences between the theoreticaland actual curves can be improved by the additional incorporation of aforward-acting control that draws in or integrates a future developmentof the theoretical value into the regulation, as well as calculates inadvance a future characteristic of the actual value with the aid of asimulation model. The simulation model used up to now in this connectionis, as mentioned a rigid simulation model.

[0030] Pursuant to the present invention, the simulation model that isthe basis of the regulation is improved in that an adaptation of thesimulation model, in particular an adaptation during the processingsequence, to varying parameters is made possible. This is achieved inthat the simulation model is split up into components, and for at leastone, but also for each, component of the model a suitable single modelis developed, and in that a measurement of at least one parameter ofthis individual model or of the individual models, as well a subsequentadaptation of parameters in the individual model, is effected during theprocess.

[0031] Due to this overall model, regulation parameters can beestablished for the individual components that are finally stored in aregulation apparatus of the overall unit. In this way, the temperaturecurve of a wafer can be controlled and regulated in a precise manner viathe individual models and their regulation parameters. The overall modelcan be adapted to varying conditions, such as, for example, variationsand changes of the measured parameters.

[0032] For the better understanding of the invention, the FIGS. 3 to 8will be subsequently considered. FIG. 3 shows a diagrammaticillustration for the determination of the radiation generated from alamp via a combination of model, measurement and adapted model, with theintegration thereof in a subordinated radiation-regulating circuit. Alamp model is initially established on a basis of the specificproperties of the lamp. Characteristic properties of a lamp to be usedas model parameters include the current flowing therethrough, theapplied voltage, its resistance, the received power and the emittedradiated power. In the static situation, the received electrical powerof the lamp is the same as the emitted power. In addition, the emittedradiated power of the lamp is correlated via the filament temperaturedirectly with its resistance. Based upon this interrelationship, one canestablish the lamp model shown in FIG. 3, as it is also described, amongothers, in J. Urban et al. in the article “Thermal Model of RapidThermal Processing Systems” in the 7^(th) International Conference onAdvanced Thermal Processing of Semiconductors—RTP'99, which to thisextent is made the subject matter of the present invention in order toavoid repetition. With this model, a single lamp is specified by threeparameters, namely its resistance characteristic R=f (T) as a functionof its temperature T, its thermal capacity C (possibly also as afunction of the temperature T), and a constant εσA that determines theirradiation power. In this connection, ε corresponds to the degree ofemission, the σ corresponds to the Stefan-Boltzmann-constant and Acorresponds to the surface area, i.e. the effective surface area of thelamp filament.

[0033] Input into the lamp model, as the adjustment value g, is thevoltage u applied to the lamp. From the voltage and the resistance R,which the lamp has in conformity with its characteristic at atemperature T, the magnitude of the current i flowing through the lampis determined. Pursuant to P_(el)=u·i there is determined therefrom theelectrical power P_(el) that circulates in the lamp. With the aid of theradiation principle of Stefan-Boltzmann, one can determine the radiationpower P_(str) emitted from the lamp with the aid of the lamp temperatureand the radiation constants (emission constants). The radiation power issubtracted for the circulating electrical power, as a consequence ofwhich one obtains the portion of the power that was converted in thelamp into heat, and that heated the filament and the lamp. By means ofthe thermal capacity c of the lamp, that is essentially prescribed bythe dimension of the filament wire, a new temperature of the lamp iscalculated. This is illustrated in FIG. 3 by the 1/c and by the integralelement. With the aid of the new temperature, a new filament resistanceR of the lamp, and therefrom the converted lamp power P_(el), isredetermined, and in addition the emitted lamp radiation P_(str) isredetermined. In this manner, the influence of the adjustment value gupon the radiation power P_(str) emitted from the lamp is determined, inparticular, the dynamic characteristic of the lamp is described.

[0034] In a following step, the parameters taken up in the lamp modelfor a prescribed lamp are measured. In this way, the model can beoptimized and can be established for a specific lamp. In particular, thedependence of the resistance upon the filament temperature, the thermalcapacity C of the filament, as well as the constants εσA are determined,whereby c, ε and A can also be determined as a function of thetemperature. Optimally, ε and A can also be adapted to the temperature.The determined parameters are inserted into the lamp model, resulting ina specific model for the lamps.

[0035] The use of the lamp model of FIG. 3 is illustrated in aregulating circuit 20 in FIG. 4. In the regulating circuit 20, theradiated power P_(str) (here as monitored parameter of the lamp model)calculated on the basis of the lamp model 25 is compared one time withthe actual lamp radiation h measured via a pyrometer 26. The differencebetween calculated and measured lamp radiation serves for the furtheroptimization of the lamp model 25 via a model-optimizing unit 28 thattakes care of an adaptation of, e.g., R, ε, A or c. In addition, thecalculated radiated power P_(lst) (=P_(str)) is compared with atheoretical radiation value e, and the lamp radiation is regulated withthe aid of the determined difference via a radiation regulator 30. Theadjustment value g given off by the radiation regulator 30, and whichcorresponds to an effective voltage, serves in addition to the controlof the lamps also as an input value for the lamp model. As gleaned fromthe above description, the lamp model, which is used with the regulationof the temperature of a wafer, can be dynamically adapted to varyingconditions in that the radiated power actually given off by the lamps iscompared with the radiated power calculated within the model. Inaddition, or alternatively, during the process one can measure otherlamp parameters m, such as, for example, current or voltage, and thelamp model can be optimized with the aid of the measured parameters.However, it is also possible to initialize the lamp model at thebeginning with the measured parameter values, and to dispense with aprocess-accompanied optimization of these values.

[0036] With the above described method it is of particular importancethat the adjustment value g, which serves for the lamp control, nolonger be determined, as was previously customary, on the basis of acomparison between the theoretical radiation value e and a measured reallamp radiation value, but rather results from the theoretical radiationvalue e and the radiated power P_(str) calculated from the lamp model.This leads to an increase of the regulating speed, and furthermore fewdisruptions result within the regulating process.

[0037] The effect and advantage of the above-described regulation isillustrated in the oscillogram images 5 a,b and 6 a,b. In the FIGS. 5aand 5 b, the lamps were controlled in a conventional manner via thevoltage as an adjustment value and without a radiation regulator (lampmodel, lamp model-optimizing unit). In this connection, FIG. 5a shows anincreasing radiated power, and FIG. 5b shows a reducing radiated power.In this connection, the voltage was varied in a stepped manner. As onecan see from the oscillogram images, the power radiated from the lampmirrors this stepped curve of the voltage only in a greatly independentmanner. Instead of a stepped alteration of the lamp radiation intensity,a wave-shaped curve can be seen.

[0038]FIGS. 6a and 6 b again show the chronological curve of the emittedradiation of a lamp, once during increase (FIG. 6a) and once duringreduction (FIG. 6b) of the lamp power. In this case, the lamps werecontrolled via the regulating circuit illustrated in FIG. 4. The curveof the radiation intensity shown in FIGS. 6a and 6 b shows a steppedcurve. A radiation regulator was utilized and the radiation intensitycalculated from the model was provided as the adjustment value. Duringcomparison of the oscillogram images of FIGS. 5a,b and 6 a,b, one shouldnote that the Y axes show different high values. This results from thefact that during the voltage jumps it is really only the voltage that isvaried as an adjustment value, whereas with the power jumps atheoretical value is prescribed for the radiated power. On the whole,lamps that are controlled (FIGS. 6a,b) via the regulating circuitillustrated in FIG. 4, represent adjustment elements having a moredynamic characteristic. With them, the temperature curve of the wafercan also be adapted more exactly to a prescribed temperature profile.

[0039] During the thermal treatment of a wafer, each individual lamp ofthe lamps of a heating apparatus can be individually regulated in thismanner.

[0040]FIG. 7 shows a preliminary control that is adapted to thecharacteristics of the wafer and includes a preliminary controlregulator that contains a model of the wafer. In the illustratedregulation, the coupling of the wafer to the lamp radiation is measured,and with the aid of the measured coupling a preliminary control adaptedto the wafer is produced. The preliminary control regulation generatesan adjustment value for the individual lamps or banks of lamps that is afunction of the temperature, the temperature alteration, the wafer size,and possibly other wafer characteristics.

[0041] A radiation i emitted and reflected from the wafer is measured inthe measuring unit 40 and is utilized for the calculation of the wafertemperature j. The radiation i emitted from the wafer is furthermorecompared in a coupling measuring unit 43 with a measured lamp radiationh, as a result of which a coupling k of the wafer to the lamp radiationcan be determined. For the determination of the coupling k of the waferto the lamp radiation, a broadband actively modulated measurement of theradiation emitted from the lamps and from the wafer is utilized. Themeasurement is effected with two pyrometers, as is known from DE-A-19855 683.7, which is attributable to the same applicant; this disclosureis to this extent made the subject matter of the present invention inorder to avoid repetition. The magnitude of the coupling k between waferand lamp radiation is a function of various parameters. For example, thewafers can even be multiply coated and/or structured with variousmaterials, which in addition to the problem of different absorptionproperties and non-homogeneous temperature distributions over the wafersurface, can also lead to interference effects of the thermal radiationat these layers. It should be noted that the term the coupling k betweenwafer and lamp radiation refers to the degree of the alternating effectbetween the wafer and the radiation field, in other words, its degree ofabsorption and emission over all occurring wavelengths.

[0042] At the point 45, the calculated wafer temperature j is comparedwith a theoretical temperature value a. A difference from theoreticalvalue and actual value is conveyed further to a temperature regulator,e.g. a PID temperature regulator 47, which on the basis of thedifference b determines a lamp control value c in a known manner. Thetheoretical value a and the calculated coupling k between the wafer andthe lamp radiation are conveyed to a preliminary control regulator 50,which delivers a preliminary control value d as a function of the wafercharacteristic k. The preliminary control value d, and the output valuec of the temperature regulator, are added at the point 54 to anadjustment value e, so that the actual adjustment value e results fromcalculations that were determined on the basis of the last measurement.In this connection, the basic model can also contain other parameters ofthe chamber, the holding device or the lamps, such as, for example, thequartz temperature, ambient temperature, etc. The adjustment value e isconveyed further to the regulator 55 a, 55 b for the upper and lowerbank of lamps.

[0043] All of the lamps disposed above the wafer are combined to theupper bank of lamps 7, and the lamps disposed below the wafer arecombined to the lower bank of lamps 8. Each of the n lamps of the upperand lower bank of lamps has an individual regulating circuit (LCL) aswas described in conjunction with FIG. 4. During the heating up in ahomogeneous lamp field, the edge regions of a disc-shaped wafer heat upmore intensely than does the center of the wafer. For the achievement ofa homogeneous temperature distribution over the wafer, individual lampsof the banks of lamps must therefore be radiated very differently. Forthis purpose, control tables (LCT) are provided for the individuallamps. With the aid of the control tables, the radiation intensity ofeach individual lamp is set during a thermal treatment. The adjustmentdevices required for this precede the regulating circuits of lamps. Theyare controlled via the adjustment value e, and take care of a desiredlamp radiation h. Since the respective lamps exhibit a different dynamiccharacteristic in different situations, it is particularly advantageousthat each lamp with the aid of its individual characteristic, becontrolled with an individual regulating circuit pursuant to FIG. 4. Inthis way, a more homogeneous heating up of the wafer is achieved,especially in the edge regions. Due to the measured parameters h and l,which provide an indication about the coupling of the wafer to the lampradiation, one obtains information concerning the model parameters ofthe lamp model that can be adapted thereto. In particular if the lampsare arc lamps, this method is very advantageous. It should be noted thatthe control tables (LCT) themselves can again be described by anindividual model that in turn can be monitored and adapted via at leastone parameter (e.g. the radial wafer temperature).

[0044] Since the wafer radiation i is the value that is to be regulated,because it permits an indication about the wafer temperature, and thecoupling measuring unit 43 compares this radiation i with the lampradiation h, what is involved is a control having feedback coupling. Thelamp radiation h itself is not regulated in the sense understood here,with its aid the value i that is to be regulated is merely brought to adesired value. For this purpose, the lamp radiation h can in principleassume any course that leads to the prescribed value of the parameter ithat is to be regulated; it is only an auxiliary parameter. In contrast,the wafer radiation j that is to be regulated is supplied to themeasuring unit 40. Here one sees a regulation in the above-definedsense.

[0045] Aging effects of lamps due to long service life can be rapidlycompensated for without great expense by a simple adaptation of theirmodel with new parameter values. A dynamic adaptation of the lampparameters in a lamp model with the aid of measured parameters is alsovery advantageous during a possible exchange or replacement of lamps. Upto now, in such a case a new model having appropriate tables had to beprepared. During the dynamic adaptation, however, the lamp can beautomatically measured and the model can automatically adapt itself. Bymeans of such a model adaptation, the lamps can also advantageouslyremain in use for a longer period of time. Furthermore, monitoredparameters, such as, for example, the P_(str) from FIG. 4, or individualmodel parameters or model parameters dependent thereon, can serve formonitoring the rapid heating unit, so that, for example, a replacementof lamps can be indicated if individual model parameters are outside ofpredefined or adapted threshold ranges.

[0046] With the preliminary control illustrated in FIG. 7, only thecoupling of the underside of the wafer to the lamp radiation is takeninto account.

[0047]FIG. 8 shows a system with which, in addition to the coupling ofthe underside of the wafer, also the coupling of the upper side of thewafer to the lamp radiation is taken into account. In FIG. 8 the samereference symbols are used as in FIG. 7 to the extent that the same orsimilar elements are concerned.

[0048] A separate observation of the coupling is particularlyadvantageous with wafers where the upper side and the underside havedifferent material coatings and therefore the optical characteristics ofthe wafer are different on both sides. In particular in thesemiconductor industry, in many cases the front sides of the wafer areprovided with one or more layers of different materials, while the backsides of the wafer are not treated. In addition, one of the surfaces canbe provided with microscopic structures, while the other surface isflat. If one takes these differences into account in two differentmodels for the preliminary control, the regulation of the wafertemperature can be improved still further. Since the coupling of thewafer to the lamp radiation results from an average value of the frontand the rear side, the preliminary control value can be determined fromthe average value of the two coupling measurements that are independentof one another.

[0049] As is illustrated in FIG. 8, the radiation h emitted from theupper and from the lower banks of lamps are determined separately, andare relied upon for a determination of the coupling between lampradiation and wafer. From these values there result differentadaptations of the forward acting regulation for the upper and the lowerlamp banks in the preliminary control regulators 50 a and 50 b.Furthermore, there results a different control of the upper and lowerbanks of lamps via a distribution unit 56.

[0050] Due to the different determinations for the adjustment values ofthe lamp radiation for the upper and lower lamp banks, a more uniformheating up of the front and rear sides of the wafer 2 is ensured. Thisis particularly advantageous for very small structures.

[0051] The invention has previously been described with the aid ofpreferred embodiments of the invention, without thereby being limited tothese embodiments. For example, pursuant to a further embodiment datatransmission devices as well as computing times of individual systemcomponents can be taken into account and can flow as parameters into themodel for the preliminary control. The measurement of unit parametersthat have no direct relationship to the adjustment value can also beadvantageous. For example, impurities or contaminations of the quartzchamber that occur during the course of the process, and that affect thetransmission of the lamp radiation, can be provided in the model bysuitable parameters that are then detected by measurements, e.g. byreflection or transmission measurements, and then affect the regulatingcircuit. For an ideal temperature control of the wafer, as manyindividual components of the system as possible should be taken intoaccount, whereby here a compromise must be found between regulatingexpense and success. Furthermore, as above with the aid of the lampmodel or the (individual) models, system monitoring functions such as,for example, monitoring integrals can be integrated. Finally, theindividual features of the above-described embodiments can be combinedwith one another.

1. Method for the thermal treatment of objects in a heating unit,especially semiconductor wafers in a rapid heating unit, with which theobjects are thermally treated with a prescribed temperature course andthe temperature of the object is regulated with a temperature regulationand a forward-acting control that is based upon a simulation model ofheating apparatus and object, characterized in that the simulation modelincludes at least one individual model that includes components of theheating apparatus and/or of the object, and in that at least oneparameter of at least one of the individual models is monitored duringthe thermal treatment and in that the simulation model is adapted to atleast one monitored parameter.
 2. Method according to claim 1,characterized in that the object is irradiated with at least one heatinglamp.
 3. Method according to claim 2, characterized in that for at leastone heating lamp an individual model is provided, and in that operatingparameters, especially the irradiated heating power, of the heating lampare monitored.
 4. Method according to one of the preceding claims,characterized in that parameters of the object that is to be treated,especially the optical characteristics thereof, are monitored.
 5. Methodaccording to claim 4, characterized in that the coupling of the objectto the heat radiation is determined.
 6. Method according to claim 4 or5, characterized in that the parameters on opposite sides of the objectare determined separately from one another.
 7. Method according to oneof the preceding claims, characterized in that data transmission timesand/or computing times are determined.
 8. Method according to one of thepreceding claims, characterized in that temperatures of the object under400° C. are calculated subsequently.
 9. Apparatus for the thermaltreatment of objects (2), especially semiconductor wafers with a heatingdevice (1), especially a rapid heating device, a regulating unit havinga PID regulator (47) and a forward-acting regulator (50) that utilizes asimulation model of heating device (1) and object (2), characterized byat least one monitoring unit for the sensing of parameters of componentsof the heating device (1) and/or or the object (2), which parameters arerelevant for the simulation model, for the comparison of the measuredparameters with the parameters of the simulation model and for theadaptation of the parameters of the simulation model to the measuredparameters.
 10. Apparatus according to claim 9, characterized by atleast one heating lamp.
 11. Apparatus according to claim 10,characterized in that the monitoring unit is provided with at least onesensor (10) for the measurement of operating parameters, especially ofthe irradiated heating power, of at least one heating lamp. 12.Apparatus according to one of the claims 9 to 11, characterized in thatthe monitoring unit is provided with at least one sensor (11) for themeasurement of parameters of the object (2) that is to be treated,especially the optical characteristics thereof.
 13. Apparatus accordingto claim 12, characterized in that two sensors are provided in order todetermine the parameters on opposite sides of the object (2).